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Article
The Surface Hardness Measurement of Stone and Improved Die Stone After the Addition of a Mixture of Chemical Additives with Different Proportion

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Abstract

Background: Incorporation of chemical additives has long been a technique used to improve properties of the gypsum products. The purpose of this work was to study the effects of adding a combination of gum Arabic and calcium hydroxide to a type III dental stone and type IV improved die stone with different proportion. The effect on water/powder ratio, and surface hardness was determined.Material and method: Both material stone and die stone were blended with two proportion of additives so that each material was mixed twice but with different proportion of gum Arabic (0.1% and 0.2%) and calcium hydroxide (0.5 % and 0.3%). Data for hardness were subjected to two-way analysis of variance.Results: The results revealed that the chemical additives were reduced the water requirements of gypsum products so that the reduction of water lead to increase the density of mixture that sets harder. For type III dental stone the additives significantly improved the surface hardness, while for type IV improved die stone the surface hardness was not enhanced except it was designed to be mixed at low water/powder ratio, and in some instances a reduction in hardness was observed, especially at the most reduced water / powder ratio (0.18)


Article
Evaluation of Some Physical Properties of Die Stone Made From Local Raw Gypsum Material

Authors: Lamia T Rejab --- Salwan F Al-Hamdani --- Mohammed Y
Journal: Al-Rafidain Dental Journal مجلة الرافدين لطب الأسنان ISSN: 18121217 Year: 2012 Volume: 12 Issue: 20 Pages: 309-315
Publisher: Mosul University جامعة الموصل

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Abstract

Aim: The aim of this study was to prepare die stone material by dehydration of the local natural raw gypsum in boiling with 30% calcium chloride solution , and then evaluated some physical properties of this prepared die stone. Materials and methods : The values of some physical properties of the pre-pared die stone in boiling with 30% calcium chloride solution which are water/powder ratio, setting time, and compressive strength were compared with that of three types of gypsum products commer-cial die stone, Elite type III dental stone and Iraqi plaster. The data were collected , mean and standard deviation were determined. Statistically, (ANOVA) and Dunnett Pairwise Multiple Comparison test were carried out to determine the significant differences at p≤ 0.05 Results: Results showed that there were no significant differences between the locally prepared die stone and the commercial one at p≤ 0.05 in water/powder ratio and setting time values, but it was significant difference in compressive strength. But there are a significant difference between the physical properties of the locally prepared die stone and Elite type III dental stone and Iraqi plaster. Conclusions: The results showed the physical properties of the locally prepared die stone approach the physical properties of the commercial product according to the recommendation of ADA for gypsum products.


Article
Compressive strength and surface roughness of die stone cast after repeated disinfection with sodium hypochlorite solution

Authors: Sunus Al-Azzawi --- Amer M Khamas عامر خماس --- Jwad Michael جواد مايكل
Journal: Journal of baghdad college of dentistry مجلة كلية طب الاسنان بغداد ISSN: 16800087 Year: 2010 Volume: 22 Issue: 3 Pages: 27-33
Publisher: Baghdad University جامعة بغداد

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Abstract

Background: The transmission of oral pathogen to impression and subsequently on to gypsum cast has beendemonstrated, and dental stone cast have to be disinfected to prevent the transmission of infectous disease, thisinfection process may affect some physical or mechanical properties of the cast. The aim of the study was toevaluate the compressive strength and surface roughness of type IV dental stone cast after repeated immertion inand sprying using (0.5%) sodium hypochlorite disinfectant solution.Materials and methods: A total of (42test blocks) were prepared and divided to (3) three groups (14each) (controlspray and immersion) for the surface roughness test. These were subdivided into (2) groups (7) each to be testedafter (24 and 48 hours) the same distribution of the test block were followed for the compressive strength test. Foreach test 1/3 of the test black immersed in the disinfectant solution for 30 minutes then allowed 24 hours for be eachdrying this was repeated 5times before being tested, 1/3 of the specimens were sprayed with the disinfectant 5 timesin an interval of 24 hours for bench drying the last 1/3 blokes were the control.Results: Immersing or spraying with hypochlorite solution significantly decreased the compressive strength after 24hours and increased after 48 hours. As for the surface roughness the results showed that both spraying and immersionsignificantly increased the value of the roughness, with immersion as a higher value. Spraying with (0.5%) sodiumhypochlorite solution provide smoother dental stone casts surfaces and adequate compressive strength whenallowed for (48hours) compared to immersion group bench drying.Conclusion: Dental stone casts disinfected by immersion method showed a higher surface roughness than thosedisinfected by spraying.


Article
Evaluation of the Effect of Microwave Irradiation and Die Hardener Application on Surface Hardness of Type IV Dental Stone

Authors: Suha Fadhil Dulaimi سهى فاضل دليمي --- Lateef E. A. Al-Jorani لطيف عيسى الجوراني
Journal: Tikrit Journal for Dental Sciences مجلة تكريت لعلوم طب الاسنان ISSN: 20731213 Year: 2016 Volume: 4 Issue: 2 Pages: 128-135
Publisher: Tikrit University جامعة تكريت

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Abstract

Type IV dental stone play an important role during fabrication ofindirect dental restoration. It should be accurate in every respect,dimensionally stable over time, hard enough to with standfabrication process resistant to the inadvertent abrasions caused byfabrication. The aim of present study was to evaluate the effect ofmicrowave irradiation and die hardener application on surfacehardness of type IV dental stone. Two commercial brands of typeIV dental stone (Spofadental/ Czech, Zhermack/ Italy) wereevaluated. 30 samples were prepared from each brand and left todry for 24hr. After that divided into three groups, control group(10 samples without treatment), 10 samples subjected tomicrowave irradiation at 650 watt output power and 2450 MHZfor 10 mint. And 10 samples painted with die hardener. Surfacehardness measured with Shore C (Durometer, Digital hardnesstester). The die hardener application not affect surface hardness ofboth brands (P>0.05). However microwave irradiation increasesurface hardness of Spofadental Type IV dental stone. But reducesurface hardness of Zhermack Type IV dental stone. After 24hr. ofpouring Type IV dental stone (Spofadental / Czech, Zhermack /Italy) die hardener application not affect surface hardness.However surface hardness of Spofadental Type IV dental stonemay be improved with microwave irradiation. But Zhermack TypeIV dental stone showed reduction in surface hardness aftermicrowave irradiation.

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